This invention relates to the field of temperature measurement and, more particularly, to apparatus and method for remote temperature measurements, particularly of reactions in microwells, and for calibration of heating means.
Work done in the microelectronics industry has resulted in a body of techniques that have come to be known generally as "micromachining". A decade ago this was just beginning to burgeon (see Angel et al., Scientific American, Vol. 248, 44-55, 1983). Today miniature processing devices incorporated into chip structures are fairly common and components are sized on a microscale which by definition is between 0.1 .mu.m and 500 .mu.m. Such small apparatus is of great benefit in microbiology. Assays, using micro processing methods, permit the use of small volume samples held in miniature containers (hereinafter "microwells") thereby improving heat transfer, mixing and reaction efficiency, reducing costs by stocking smaller quantities of expensive reagents and permitting greatly reduced and less costly sample volumes. Single-use, inexpensive and disposable structures are avidly sought.
Capillary electrophoresis, for example, is a field of great activity, as is the development of small scale methods for polymerase chain reaction (PCR). Processing channels for capillary electrophoresis may be on the order of 15 .mu.m deep by 100 .mu.m wide and processing wells for PCR may be about 0.5 mm deep and 2 mm square to hold samples with a volume of about 2 .mu.L. These microwells must be supplied with heating and cooling means and the temperatures in the wells must be controlled with precision.
PCR involves repeated cycling between several elevated temperatures (see U.S. Pat. Nos. 4,683,195 and 4,693,202). As a result, measurement and control of temperature is paramount. When performed on a microscale, measurement of the temperature in the micro wells becomes exceedingly difficult. Thermometers are too large. Thermocouple probes, thermistors and resistance temperature devices (RTDs), ordinarily used in calibrating and monitoring temperatures in small spaces, are large enough in comparison to the volume involved in a microwell to intrude on the test accuracy. While it is possible to fabricated these devices as an integral part of the apparatus to obviate the intrusion, they are expensive to calibrate and only provide temperature of a local region since they are restricted to an edge or side of a well. In addition, because the temperatures involved are below 100.degree. C., remote sensing methods which rely on infrared emanations are not effective.
Thus, it is an object of this invention to provide a remote sensing method and apparatus for measuring and/or calibrating temperatures in the range around or below 100.degree. C. in microwells. While the inventive method is particularly adapted for use with microwells, it will be appreciated that the method may be used with a variety of apparatus and thus is not limited to this single use.